1. School of Mathematics and Statistics, Central South University, Changsha, P.R. China
2. Department of Mathematics, AIR University, Islamabad, Pakistan
3. Department of Computer Science and Mathematics, Lebanese American University, Beirut, Lebanon
4. Department of Mathematics, Siirt University, Art and Science Faculty, Siirt, Turkey
5. Department of Mathematics, Near East University, Mathematics Research Center, Nicosia/Mersin 10, Turkey